1. Technical Field
The present invention relates to a speed control apparatus for a switched reluctance motor.
2. Description of the Related Art
In accordance with the development of industries, a high performance and multi-functional electromotive device has been demanded in order to maintain a high cultural life. Therefore, an electric motor having a simpler mechanical structure, a cheaper cost, and more excellent efficient and output characteristics as compared to the existing electric motor has been demanded.
Among currently known electric motors, a switched reluctance motor (SRM) has been widely used in industrial systems and home appliances due to a simple and firm mechanical structure, an excellent traction torque, a low manufacturing cost, and a cheap maintenance cost.
This SRM is cheap due to a simple structure, is robust to an environmental factor, and has a high generation torque per unit area. However, it is necessary to detect information on a rotor position in order to control a speed of the SRM in industrial applications.
The reason is that the SRM is driven by a pulse type excitation power and a change in magnetic resistance according to saliency of a rotor and a stator, that is, a reluctance torque, such that it is required to continuously apply a pulse excitation power for each predetermined rotation period of a rotor, unlike a general alternate current (AC) electric motor obtaining rotational force by a rotor system.
As the prior art for detecting a rotor position according to this demand, there is a method using a sensor such as an encoder, a resolver, or the like, as disclosed in Japanese Patent Laid-Open No. 2004-364498, or the like. However, it is difficult to use this prior art in a poor environment in which a temperature rises or a large amount of vibration occurs since the used encoder, resolver, or the like, is sensitive to environmental factors such as temperature, vibration, and the like. In addition, this prior art causes an increase in cost due to occurrence of an additional cost.
Therefore, in order to solve this problem, an SRM control method using a sensorless algorithm has been developed.
As the prior art associated with the SRM control method using a sensorless algorithm, there is a sensorless scheme of the SRM using a magnetic flux. In this scheme, a magnetic flux of the phase winding calculated in consideration of a voltage applied to a phase winding, a current flowing in the phase winding, and a resistance value of the phase winding has been used.
However, this prior art may not detect a rotor position in a stop state and has low estimation precision in a low speed period.
In addition, according to the prior art, the phase winding voltage, current, and resistance considered at the time of calculation of the magnetic flux include an error, (particularly, due to a variation in a voltage drop and a variation in the phase winding resistance according to a change in a temperature of a switching device), such that an error continuously occurs in an estimation position.
As a result, due to this error in the estimation position, sensorless performance of the SRM is significantly deteriorated, and when the error is continuously increased, the SRM may also not be operated normally.